In general, as shown in a partially perspective view of FIG. 4, blades 2 are inserted to be mounted on the outer circumference of a ring-shaped disk 1 in a gas turbine. Both the ring-shaped disk 1 and the blades 2 are configured to rotate at a high speed. The ring-shaped disk 1 is made of a Ni-based alloy (for example, Inconel 718 or the like) having excellent heat resistance. The Ni-based alloy has a composition that includes, in terms of percent by mass (hereinafter, % indicates mass percent), 50.00 to 55.00% of Ni, 17.0 to 21.0% of Cr, 4.75 to 5.60% of Nb, 2.8 to 3.3% of Mo, 0.65 to 1.15% of Ti, 0.20 to 0.80% of Al, and 0.01 to 0.08% of C, with the balance being Fe and inevitable impurities, and has a microstructure in which δ phase particles are dispersed in a matrix thereof. The ring-shaped disk is manufactured as follows. First, a preformed ring material 3 shown in a perspective view of FIG. 2 is produced from a Ni-based alloy having the above-mentioned composition. The preformed ring material 3 is interposed between an upper die 4 and a lower die 5 as shown in FIG. 3, and a downward pressure in the direction of arrow A and an upward pressure in the direction of arrow B are exerted on the upper die 4 and the lower die 5, respectively. In this way, the preformed ring material 3 is subjected to die forging; and thereby, a ring-shaped forged material 9 is produced. Then the ring-shaped forged material 9 is machined so as to have a predetermined shape of the ring-shaped disk. As a result, the ring-shaped disk is produced (Non-Patent Documents 1 and 2).
Recently, with the size of aircrafts increasing, gas turbines of aircraft engines are getting larger while getting higher power. Therefore, components used in gas turbines for aircraft engines are required to have much higher strength. In particular, in response to the increasing size of the gas turbines, greater centrifugal force is applied to the ring-shaped disk. In addition, a difference in temperature between the center portion and the outer circumferential portion of the ring-shaped disk becomes larger; and thereby, a thermal stress applied in the circumferential direction becomes greater. Furthermore, if the ring-shaped disk is damaged due to its insufficient strength, here is a concern that the damage may lead to an aircraft trouble. Therefore, the ring-shaped disk is required to have much higher strength.
In addition, in the related art, the ring-shaped disk is manufactured by die forging as described above; and therefore, with the size of the ring-shaped disk increasing, much larger die forging machines are required. However, a large-sized die forging machine not only incurs a high cost in itself but also requires strengthening of the foundations on which the die forging machine is intended to be constructed. Therefore, it is inevitable that costs increase as the size of the die forging machine increases.